Special Relativity derived heuristically from a Correspondence Principle

We present a derivation of special relativity based on a single heuristic hypothesis: that the Lagrangian of relativistic dynamics must reduce, at first order in v/c, to the classical Newtonian Lagrangian. From this requirement alone, without postulating either the covariance of physical laws or the invariance of the speed of light, the existence of a limiting velocity, the relativity of time, and the geometric structure of Minkowski spacetime emerge naturally. A suggestive structural connection with the foundational relation of quantum mechanics, E = hν, is also discussed.